Tracking separation between an object and a surface using a reducing structure

Abstract

Tracking separation between an object and a surface involves illuminating the surface and reducing the collection angle of light that reflects off of the surface in response to a change in separation between the object and the surface. Reducing the collection angle of light that reflects off of the surface causes the amount of light that is detected to be dependent on the separation distance between the object and the surface. The amount of detected light is then used as an indication of the separation distance.

1. A method for tracking separation between an object and a surface comprising:
 illuminating a surface; 
 reducing a collection angle of light that is incident on a sensor in response to a change in separation between an object and the surface; 
 detecting light subjected to the reduced collection angle; and 
 determining separation between the object and the surface in response to the detected light. 
 
     
     
       2. The method of  claim 1  wherein determining separation between the object and the surface comprises comparing a characteristic of the detected light to a lift threshold. 
     
     
       3. The method of  claim 2  wherein the lift threshold is defined in terms of light intensity. 
     
     
       4. The method of  claim 2  further including indicating a lift condition when the detected light reaches the lift threshold. 
     
     
       5. The method of  claim 1  wherein detecting light subjected to the reduced collection angle comprises detecting light with an image sensor, the image sensor including an array of individual photosensors that generate navigation information. 
     
     
       6. The method of  claim 5  wherein determining separation between the object and the surface comprises comparing a characteristic of the navigation information to a lift threshold. 
     
     
       7. The method of  claim 6  further including indicating a lift condition when the compared characteristic of the navigation information reaches the lift threshold. 
     
     
       8. The method of  claim 7  wherein the characteristic of the navigation information is one of total intensity, bright pixel count, dark pixel count, and intensity gradient. 
     
     
       9. The method of  claim 1  wherein reducing the collection angle involves subjecting the reflected light to an aperture. 
     
     
       10. The method of  claim 1  wherein reducing the collection angle involves subjecting the reflected light to a lens. 
     
     
       11. An optical navigation device comprising:
 a light source configured to illuminate a surface; 
 a sensor configured to generate navigation information in response to light that reflects off of the surface; 
 a reducing structure, located in an optical path between the light source and the sensor, configured to reduce a collection angle of light that is incident on the sensor in response to a change in separation between the optical navigation device and the surface; 
 a navigation engine configured to generate lateral position information relative to the surface in response to the navigation information; and 
 lift detection logic configured to generate lift information related to the optical navigation device relative to the surface in response to the navigation information from the sensor. 
 
     
     
       12. The system of  claim 11  wherein the lift detection logic is further configured to compare a characteristic of the navigation information to a lift threshold. 
     
     
       13. The system of  claim 12  wherein the lift detection logic is further configured to indicate a lift condition when the compared characteristic of the navigation information reaches the lift threshold. 
     
     
       14. The system of  claim 13  wherein the characteristic of the navigation information is one of total intensity, bright pixel count, dark pixel count, and intensity gradient. 
     
     
       15. The system of  claim 13  wherein the generation of lateral position information by the navigation engine is suspended when the lift detection logic indicates a lift condition. 
     
     
       16. The system of  claim 11  wherein the reducing structure comprises an aperture. 
     
     
       17. A method for tracking separation between an optical navigation device and a surface comprising:
 illuminating a surface with light from an optical navigation device; 
 reducing a collection angle of light that is incident on a sensor in response to a change in separation between the optical navigation device and the surface; 
 collecting navigation information from light that reflects off of the surface and is subjected to the reduced collection angle; and 
 using the navigation information to track the lateral position of the optical navigation device relative to the surface and to identify a lift condition of the optical navigation device relative to the surface. 
 
     
     
       18. The method of  claim 17  wherein determining separation between the optical navigation device and the surface comprises comparing a characteristic of the navigation information to a lift threshold. 
     
     
       19. The method of  claim 18  further including indicating a lift condition when the compared characteristic of the navigation information reaches the lift threshold. 
     
     
       20. The method of  claim 19  further including suspending the tracking of lateral position when a lift condition is indicated.